1. Field of the Invention
The present invention relates to apparatus and methods for filtering and diffusing air in an enclosed space and particularly in clean rooms and clean and ultra-clean environments.
2. Description of Related Art
Many industries are now demanding far greater purity and cleanliness standards than were ever previously required. For example, with the advent of smaller and faster semiconductors and other electronics, tolerances for contaminants have become a critical parameter in meeting standards, reducing waste, and maintaining profitability. Similarly, tighter contamination control standards are also a growing concern in a variety of other industries, such as pharmaceuticals, aerospace, food, medical products, surgical environments, etc.
To address these requirements, clean rooms and ultra-clean rooms have been developed with extremely low ambient contamination levels. Examples of such structures are disclosed in numerous patents, including U.S. Pat. Nos. 4,409,889 issued Oct. 18, 1983, to Burlseson, 4,267,769 issued May 19, 1981 to Davis et al., 4,953,333 issued Sep. 4, 1990, to Carlson, and 5,029,518 issued Jul. 9, 1991, to Austin. Moreover, smaller and less expensive environments have been developed which are extremely clean, essentially human-free, housings for process equipment, such as mini-environments and micro-environments in the semiconductor industry and those employing barrier isolation technologies in the pharmaceutical industry.
In order to maximize the benefits of these new ultra-clean areas, every aspect of the environment must be carefully controlled and monitored. Central to every clean room facility is an effective ventilation and air filtering system which tightly contains the size and number of air borne particles. Examples of various ventilation systems are disclosed in U.S. Pat. Nos. 3,975,995 issued Aug. 24, 1976, to Shuler, 4,094,232 issued Jun. 13, 1978, to Howorth, 4,554,766 issued Nov. 26, 1985, to Ziemer, 4,929,262 issued May 29, 1990, to Balon, Jr. et al., and 5,053,064 issued Oct. 1, 1991, to Hama et al.
Among the concerns in developing an effective ventilation system is that the flow of air from ventilation conduits must be sufficiently laminar and uniformly distributed so as not to disrupt operating conditions or produce turbulence. One example of such a diffusion device is disclosed in U.S. Pat. No. 4,603,618 issued Aug. 5, 1986, to Soltis. In order to achieve proper diffusion and laminar (non-turbulent) air flow from a conventional HEPA (High Efficiency Particular Absolute) filtered air system, U.S. Pat. No. 4,603,618 forms a second plenum across the ceiling of a clean room and then installs a number of translucent diffusion panels therein. The panels include translucent fibrous sheets of controlled porosity wrapped around the edge of the panels and held in place with a clip. The fibrous sheets permit the passage of both filtered air and light from light fixtures mounted above the panels. One of the asserted advantages of such a system is that the diffusion panels are mounted in a conventional T-bar grid without the use of gaskets or sealants.
While the diffusion panels disclosed in U.S. Pat. No. 4,603,618 may function adequately well for their stated purposes, they suffer from a number of serious deficiencies. First, if not properly controlled, the fibrous sheets employed in these panels are believed to shed fibers or particulates, leading to a certain amount of contamination from the panels themselves. Second, the use of a non-woven material also tends to be less uniform in mass variation which leads in turn to less uniformity in flow. Third, the intentional loose fitting of the diffusion panels into conventional T-bar grids leaves open the risk of contamination passing around the perimeter of the panels, particularly if the panels are not prevented from vibrating in place. Fourth, the wrap-around fabrication method employed in the Soltis patent tends to be burdensome to construct and often leads to uneven tensioning of the diffusion panel in the frame. Other problems with the Soltis diffusion panels are believed to include: inability to filter small and sub-micron particles adequately, such as those released from even the cleanest ULPA filters or duct mechanisms; use of a relatively large grid support structure downstream reduces performance of the diffusion material; lack of adequate structural integrity in panel design-leading to possible leakage or failure; and inability to prevent water contamination.
Another problem not addressed by any of the above references is how to provide contamination protection in micro-environment and mini-environment clean facilities. In these instances, each contained environment can be supplied by its own air duct. As such, the air stream tends to be more direct and focused and in greater need of redistribution. Since these facilities are normally employed under extremely clean conditions, a greater degree of filtration is also ordinarily required for these systems.
Accordingly, it is a primary purpose of the present invention to provide a diffusion panel for a clean or ultra-clean environments which minimizes contamination by providing a high degree of diffusion and filtration efficiency.
It is a further purpose of the present invention to provide such a diffusion panel which can be tightly installed in a variety of air filtration ducts and which is not prone to vibration or seepage of air around the perimeter of the panel.
It is yet another purpose of the present invention to provide such a panel which is an effective barrier to many different contaminates, including condensates and other liquids which may be present in an air supply duct.
It is still another purpose of the present invention to provide such a panel which is suitable for use in filtering and diffusing air in mini- and micro-environment facilities.
It is a further purpose of the present invention to provide a method of constructing such a diffusion panel which is straightforward and readily accommodates providing even tensioning of the diffusion membrane.
These and other purposes of the present invention will become evident from review of the following specification.